The present invention relates generally to scrapers for removing a variety of materials and more particularly to bladed, antiscratch, multistate water precipitation removing tools for delicate aircraft airfoil surfaces. A frame, a handle, and a plurality of scraping members comprise my tool and permit the removal of snow, slush, ice, frost, and water from such surfaces, and the polishing of more-difficult-to-remove frost thereon, without any damage thereto.
Removal of snow, ice, frost, and slush from airplane airfoil surfaces is a well known flight safety necessity. As serious as the additional weight burden imposed by solid-state precipitation is the associated destruction of lift caused by (1) frost, snow, and ice disrupting the laminar flow of air over wing and tail surfaces, and (2) the resulting increase in parasitic drag produced by the rough airfoils. A mere 1/16" of rough, heavy frost, for example, can markedly reduce the boundary layer kinetic energy of air moving over a wing, disastrously decreasing lift. However, this same 1/16" of frost, once polished, has much less effect on aircraft performance. Two options then exist: (1) removing all precipitation from the wing surface (the preferred method); or (2) polishing smooth by mechanical means any residual frost that cannot be completely removed from wings and stabilizers. Large, commercial airline companies generally employ chemical deicers. That is, alcohols or other deicing chemicals, often heated, are sprayed on the wing and tail surfaces. However, these fluids are too heavy to carry on board an airplane in quantities necessary for effective deicing of large wings and tails and are also dangerous to transport. Unfortunately, small and/or remote airfields do not ordinarily have the required deicing agents or spray equipment. Corporate and private aircraft owners, therefore, have had in the past to utilize relatively crude mechanical means (e.g.,brooms, rope, burlap bags, and even the edges of credit cards) for snow and ice removal. Also, in the past, water and slush have had to be removed by primitive means (e.g., compressed air, rags, industrial floor squeegees, and mops) because liquids left on airfoils will turn to ice as an airplane taxis or takes off but specialized implements were not available for such tasks.
Pending U.S. patent application Ser. No. 424,388 "Multistate Precipitation Removal Tool" filed Sept. 27, 1982 by Bruce M. Adams, the disclosure of which is hereby incorporated herein by reference, describes several embodiments of a precipitation removal tool fabricated from elastomeric and silicone rubber materials which maintain their flexibility and hardness characteristics over the broad temperature range for which airfoil deicing is necessary. The preferred embodiment of tool of the present invention has some of its scraping members fabricated out of the same materials, but is designed to be more efficient for larger airfoils than the tool taught therein. It has larger scraping and squeegeeing edges so that a stiff frame or support is required to hold the more flexible scraping members in the correct orientation. Moreover, the tool head shape has been chosen to provide another efficient snow-shoveling capability. That is, the obtuse angle of the supporting frame permits the operator of the tool to use handles of substantial length without having to exert large downward force on the tool head when removing snow since the weight of the snow forces the tool head against the airfoil surface. Patent application Ser. No. 424,388 describes further the commercially available elastomers with properties between plastics and rubbers, and silicone rubber, which have been found to be particularly effective as scraping blade members for removing ice, snow, water, and slush from delicate surfaces and polishing difficult-to-remove frost thereon without damage to these surfaces. E. I. duPont de Nemours and Co. Tradename `Hytrel` polyester elastomers are available in compositions soft enough to squeegee water from shaped surfaces, in compositions of intermediate flexibility suitable for polishing frost thereon, and in compositions hard enough to scrape off crusty snow and light ice without damaging airfoil surfaces over the important temperature range which includes ground temperatures most often encountered during and after winter storms, i.e., from about 0.degree. to -40.degree. C. Dow Corning DC55 silicone rubber has been useful for the preferred embodiment of the instant precipitation removal tool as the squeegee blade member.
Three relevant bulletins from E. I. duPont de Nemours and Co. describe the `Hytrel` product line: HYT-501A, "Mechanical Properties of `Hytrel`"; HYT-001A, "Types, Properties, and Uses of `Hytrel`"; and E-26276, "Engineering Guide to the duPont Elastomers," the disclosures of which bulletins are hereby incorporated herein by reference. The third of these publications lists 23 uses for these materials, none of which includes my invention. Although these bulletins list the properties of `Hytrel`, these properties should not be regarded as restricting the materials from which my tool is fabricated to `Hytrel`.
The following items are also believed to be important:
1. U.S. Pat. No. 2,904,806 and U.S. Pat. No. 2,904,807, both issued to H. Obergfell on Sept. 22, 1959 describe window cleaners with a plastic scraping member and a rubber squeegee member. The claims recite window cleaner elements or members, respectively, which when read in view of the spectifications, teach plastics which do not scratch glass and rubber squeegee blades. No mention is made of the temperature range for which the invention is to be used. Since most plastics and rubber compounds will not scratch glass, but most will damage delicate airfoil surfaces, especially at low temperatures, the present invention is believed to be nonobvious over these patents. Therefore, most plastics and rubber materials suitable to the window cleaning arts are unsuitable for the purpose intended for my invention. Further, all of the scraping members of my tool are able to ride over rivets and other small protrusions located on airfoil surfaces without damage either to the tool or to the protrusions. Moreover, the particular design using certain obtuse angles for the relative location of the two stiffer scraping members of the present invention, and the particular range of widths, lengths and thicknesses selected for the rectangular regions of the tool head has been found to permit the use of long handles when the tool is used for snow removal since the weight of the snow forces the snow removal scraping member into close contact with the airfoil surface to be cleaned. Finally, an intermediate flexibility and hardness blade member in a particular design of my tool is useful for removing and/or polishing frost. This scraping member is applied in a substantially perpendicular manner to the surface. Both Obergfell patents show squeegee and scraping members angled forwardly. Frost polishing is not a function that a window cleaning tool would be expected to perform, and indeed there are no teachings in the Obergfell patents directing one to such a function.
2. U.S. Pat. No. 3,540,071 issued to I. W. Jorgensen on Nov. 17, 1970 for a cleaning tool and U.S. Pat. No. 3,787,921 issued to Robert G. Feldmann on Jan. 29, 1974 both teach an abrasion resistant automobile scraping member and a resilient or flexible wiping member. Again, no mention is made of a particular choice of blade materials which would allow the use of this cleaning tool for delicate airfoil surfaces. The only stated caution for the choice of the scraping members is that they will not scratch nor mar glass surfaces. Further, as discussed hereinabove for the Obergfell patents, no teachings nor claims are provided therein for polishing frost thereon, nor riding over small protrusions affixed thereto (e.g., rivets), nor for efficiently removing snow from such surfaces. In fact, the use of the same material for all members of the complicated frame of Jorgensen's and Feldmann's scraping tools as are used for the ice scraping members, which are both further shown to possess a sharp edge, teaches away from the present invention which teaches the use of softer and more flexible blade members which generally cannot retain sharp edges and are, in fact, designed so as not to incorporate them. Finally, both the scraping and squeegeeing members of Jorgensen's and Feldmann's tools are angled forwardly. This is significantly different from the requirements of the present invention.
3. U.S. Pat. No. 3,773,375 issued to George R. Nehls on Nov. 20, 1973 teaches a snow removal device with one metallic scraping blade and one rubber blade substantially in-line. Since the Nehls patent teaches a metallic scraping member, this patent teaches away from the present invention of a scraper/squeegee/polisher tool.
4. Finally, U.S. Pat. No. 2,946,076, issued to Sidney C. Morgan on July 26, 1960, describes a U-shaped ice-scraping tool constructed of a single material such as vinyl plastic, hard rubber, or sheet Plexiglas which will not scratch glass. This patent does not teach the present invention because: (1) vinyl plastics and Plexiglas will damage airfoil surfaces; (2) hard rubber, when cold, is of value only for scraping ice and pushing snow; and (3) the U-shaped ice scraping head is not well suited for removing snow or squeegeeing liquid accumulations from large surfaces.